x
The second time, I changed it on B.
y
The second time was changed on C.
12-x-y
Time.
Change 1 time on the first machine, and the currency will increase.
2- 1
=
1
Change 1 time on two machines, and the number of coins will increase.
4- 1
=
three
Change 1 time on C machine, and the number of coins will increase.
10- 1
=
nine
Enumerable equation: x+3y+9( 12-x-y)
=
8 1- 1
Binding: 4x+3y
=
14
, available: y
=
( 14-4x)/3
will
x
=
1、2、3
Substitution tests were conducted separately,
Available: Positive integer solutions only
x
=
2
，y
=
2
; Yes: 12-x-y
=
eight
So, he changed it on the first machine.
2
The second time, I changed it on B.
2
The second time, I changed it on C.
eight
Time.